Fuel cell power generation system

ABSTRACT

A fuel cell electrical power generation system ( 1 ) is provided which is made up of components including a desulfurizer ( 3 ), a prereformer ( 5 ), an internal reforming type solid electrolyte fuel cell ( 7 ) etc. The fuel cell ( 7 ) is made up of components including an air electrode ( 31 ), an electrolyte ( 33 ), a fuel electrode ( 35 ), an air chamber ( 37 ), a fuel chamber ( 39 ), external circuits etc. The prereformer ( 5 ) operates as follows. After being flowed through the desulfurizer ( 3 ), the town gas/air is flowed through the prereformer ( 5 ) during the startup phase of the internal reforming type solid electrolyte fuel cell ( 7 ), thereby to cause partial oxidation of hydrocarbons present in the town gas to generate a partial oxidation gas which contains CO and H 2 . This partial oxidation gas is supplied to the fuel chamber ( 39 ).

TECHNICAL FIELD

The present invention relates to a fuel cell electrical power generationsystem.

BACKGROUND ART

Fuel cell electrical power generation systems having solid electrolytefuel cells are well known in the prior art.

Typically a solid electrolyte fuel cell consists of component partsincluding an electrolyte, a fuel electrode, an air electrode, a fuelchamber, an air chamber etc. The fuel electrode is mounted on onesurface of the electrolyte. The air electrode is mounted on the othersurface of the electrolyte. And the fuel chamber is defined on the fuelelectrode side and the air chamber is defined on the air electrode side,in other words these chambers are separated by the electrolyte servingas a partition wall.

During the generation of electrical power, the fuel chamber is fed H₂and CO while on the other hand the air chamber is fed air. And theoxygen in the air chamber is dissociated into oxygen ions (O²⁻) at theinterface between the air electrode and the electrolyte. The oxygen ionsmove towards the fuel electrode. Next, O²⁻ reacts with H₂ and CO in thefuel chamber at the interface between the fuel electrode and theelectrolyte, thereby generating H₂O and CO₂. At this time, thegeneration of electrical power is carried out by electrons emitted fromO²⁻.

Incidentally, in order for oxygen ions (O²⁻) to smoothly move towardsthe fuel electrode through the inside of the electrolyte, thetemperature of the electrolyte is preferably from 700 up to 1000 degreesCentigrade. To this end, the solid electrolyte fuel cell's operatingtemperature is set so as to fall in the range of 700 to 1000 degreesCentigrade.

Since the solid electrolyte fuel cell's operating temperature is 700 to1000 degrees Centigrade, this requires application of heat to the solidelectrolyte fuel cell from the outside to activate it. To cope with thisrequirement, a burner is disposed near the solid electrolyte fuel cellto raise its temperature. And during the startup phase of the solidelectrolyte fuel cell, the solid electrolyte fuel cell is preheated bythe use of combustion heat of the burner.

PROBLEMS TO BE SOLVED

The problem associated with the above prior art technique is that sincethe solid electrolyte fuel cell's operating temperature is high (700 to1000 degrees Centigrade) it takes a long time to activate the solidelectrolyte fuel cell in the past.

The present invention was made in view of the above-described drawback.Accordingly, an object of the present invention is to provide animproved fuel cell electrical power generation system having a solidelectrolyte fuel cell. More specifically, the present invention intendsto provide technologies capable of reducing the startup phase of such asolid electrolyte fuel cell.

DISCLOSURE OF INVENTION

A first invention includes a reformer through which an oxygen-containinggas and a source gas are flowed and which has a catalytic part forcausing the partial oxidation of hydrocarbons contained in the sourcegas during the flowing of the gasses. Additionally, the first inventionfurther includes a solid electrolyte fuel cell which is disposeddownstream of the reformer and which has a cell main unit whichincludes: a fuel electrode which is supplied with a partial oxidationgas which contains hydrogen generated as a result of the flowing of thesource gas and the oxygen-containing gas through the reformer; an oxygenelectrode which is supplied with an oxygen-containing gas; and anelectrolyte which lies between the fuel electrode and the oxygenelectrode, wherein an electrode reaction of the partial oxidation gasand the oxygen-containing gas is caused to take place in the fuelelectrode, the oxygen electrode and the electrolyte.

Incidentally, the temperature, at which ions are allowed to move throughthe electrolyte, is a given temperature lower than the solid electrolytefuel cell's operating temperature which is high (from about 700 up toabout 1000 degrees Centigrade).

Here, in accordance with the present invention, a supply of partialoxidation gas is provided to the fuel electrode, thereby making itpossible to heat not only the fuel electrode but also the electrolyte bythe use of the heat held in the partial oxidation gas. When thetemperature of the electrolyte rises to a predetermined degree, anelectrode reaction is caused to take place in the fuel electrode, theoxygen electrode and the electrolyte by the use of hydrogen contained inthe partial oxidation gas, thereby making it possible to startgenerating electrical power. Accordingly, the present invention makes itpossible to start generating electricity at the predeterminedtemperature lower than the operating temperature of the solidelectrolyte fuel cell.

Additionally, the electrode reaction accompanies the generation of heat.Therefore, the electrolyte is heated by making utilization of both theheat held in the partial oxidation gas and the heat associated with theelectrode reaction. Therefore, the time taken for the solid electrolytefuel cell to reach its operating temperature is reduced. Accordingly,the first invention is able to reduce the startup phase of the solidelectrolyte fuel cell.

A second invention is intended for a fuel cell electrical powergeneration system comprising:

-   -   a reformer having a catalytic part which when a source gas is        flowed therethrough converts hydrocarbons, contained in the        source gas and having a carbon number equal to or greater than        2, into methane under the presence of hydrogen, and which when        the source gas and an oxygen-containing gas are flowed        therethrough causes the partial oxidation of hydrocarbons        contained in the source gas, and    -   a solid electrolyte fuel cell which is disposed downstream of        the reformer and which has a cell main unit which includes: a        fuel electrode which is supplied with a hydrogen-containing gas;        an oxygen electrode which is supplied with an oxygen-containing        gas; and an electrolyte which lies between the fuel electrode        and the oxygen electrode, wherein an electrode reaction of the        hydrogen-containing gas and the oxygen-containing gas is caused        to take place in the fuel electrode, the oxygen electrode and        the electrolyte. And the fuel cell electrical power generation        system of the second invention performs:    -   a startup operation in which the source gas and the        oxygen-containing gas are flowed through the catalytic part of        the reformer, and a partial oxidation gas which contains        hydrogen generated as a result of the flowing of the source gas        and the oxygen-containing gas through the reformer is supplied        to the fuel electrode as the hydrogen-containing gas, and    -   a normal operation in which the source gas is flowed through the        catalytic part of the reformer and a fuel gas which contains        methane generated as a result of the flowing of the source gas        through the reformer is supplied to the fuel electrode.

As a result of such arrangement, during the startup operation, a supplyof partial oxidation gas is provided to the fuel electrode, therebymaking it possible to heat not only the fuel electrode but also theelectrolyte by the use of the heat held in the partial oxidation gas.When the temperature of the electrolyte rises to a predetermined degree,an electrode reaction is caused to take place in the fuel electrode, theoxygen electrode and the electrolyte by the use of hydrogen contained inthe partial oxidation gas, thereby making it possible to startgenerating electrical power. Accordingly, the present invention makes itpossible to start the generation of electricity at the predeterminedtemperature lower than the operating temperature of the solidelectrolyte fuel cell.

Additionally, the electrode reaction accompanies the generation of heat.Therefore, the electrolyte is heated by making utilization of both theheat held in the partial oxidation gas and the heat associated with theelectrode reaction. Therefore, the time taken for the solid electrolytefuel cell to reach its operating temperature is reduced. Accordingly,the present invention is able to reduce the startup phase of the solidelectrolyte fuel cell.

In addition to the above, during the normal operation, the reformerconverts hydrocarbons with a carbon number equal to or greater than 2into methane, in other words the fuel gas which is supplied to the fuelelectrode does not contain hydrocarbons having a carbon number equal toor greater than 2. Therefore, even when the supply amount of water tothe fuel electrode is small, there are few possibilities that carbon maydeposit on the fuel electrode. Therefore, in accordance with the presentinvention, it is possible to prevent carbon from depositing on the fuelelectrode of the solid electrolyte fuel cell.

In addition, during the normal operation, it is possible to convert thefuel gas into a reformed gas which contains hydrogen under the presenceof water in the fuel electrode of the solid electrolyte fuel cell.Therefore, in accordance with the present invention, it is possible touse such a reformed gas as the hydrogen-containing gas.

A third invention is provided with a first heat exchange means forperforming heat exchange between the source gas and theoxygen-containing gas prior to their entry into the reformer and thepartial oxidation gas discharged out of the reformer.

Incidentally, when source and oxygen-containing gases of low temperatureare supplied to the reformer, the catalytic part of the reformer iscooled by these gases. At this time, the reaction of causing partialoxidation of hydrocarbons contained in the source gas is inhibited inthe reformer.

Here, in accordance with the present invention, the first heat exchangemeans operates to effect heat exchange of the source gas and theoxygen-containing gas prior to their entry into the reformer with thepartial oxidation gas discharged out of the reformer, whereby thesesource and oxygen-containing gases are heated by the heat held in thepartial oxidation gas. This therefore prevents the source andoxygen-containing gases from cooling the catalytic part of the reformer.Consequently, in accordance with the present invention, it is possibleto cause the aforesaid partial oxidation reaction to take place activelyin the reformer.

A fourth invention is provided with a first combustion means for burningthe source gas and the oxygen-containing gas during the startup phase ofthe reformer. The fourth invention further includes a first combustiongas supply means for supplying to the reformer a combustion gasgenerated as a result of the burning of the source gas and theoxygen-containing gas in the first combustion means so that the reformeris heated.

Incidentally, when the temperature of the reformer exceeds apredetermined degree, it becomes possible to start a partial oxidationreaction in the reformer.

Here, in accordance with the present invention, the first combustion gassupply means provides a supply of combustion gas to the reformer duringthe startup phase of the reformer, whereby the reformer is heated withthe heat held in the combustion gas. This arrangement makes it possibleto increase the temperature of the reformer up to the predetermineddegree, and a partial oxidation reaction starts in the reformer.Accordingly, in accordance with the present invention, the reformer isactivated.

A fifth invention is provided with a second combustion means for burningthe source gas and the oxygen-containing gas before the electrodereaction starts taking place. The fifth invention further includes asecond combustion gas supply means for supplying to the oxygen electrodea combustion gas generated as a result of the burning of the source gasand the oxygen-containing gas in the second combustion means so that theoxygen electrode is heated.

As a result of such arrangement, the second combustion gas supply meansprovides a supply of combustion gas to the oxygen electrode before anelectrode reaction starts taking place and, as a result, not only theoxygen electrode but also the electrolyte is heated with the heat heldin the combustion gas. Accordingly, the electrolyte is heated with theheat held in the partial oxidation gas, the heat associated with theelectrode reaction and the heat held in the combustion gas. Therefore,the time taken for the solid electrolyte fuel cell to reach itsoperating temperature is reduced further. Accordingly, the presentinvention is able to reduce the startup phase of the solid electrolytefuel cell to a further extent.

A sixth invention is provided with a third combustion means for burninga source gas and a first oxygen-containing gas. The sixth inventionfurther includes a

-   -   second heat exchange means for performing heat exchange between        a combustion gas generated as a result of the burning of the        source gas and the first oxygen-containing gas in the third        combustion means and a second oxygen-containing gas different        from the first oxygen-containing gas. In addition, the sixth        invention further includes an oxygen-containing gas supply means        for supplying to either or both the reformer and the oxygen        electrode the second oxygen-containing gas heated by the second        heat exchange means.

Incidentally, when a source gas and an oxygen-containing gas are burned,water and soot may be generated as a result of the burning ofhydrocarbons contained in the source gas. Accordingly, when thecombustion gas is supplied to the fuel electrode and to the oxygenelectrode, there is a possibility that the fuel and oxygen electrodesmay deteriorate by water and soot contained in the combustion gas.

In accordance with the present invention, the second heat exchange meanseffects heat exchange between the combustion gas and the secondoxygen-containing gas and, in addition, the oxygen-containing gas supplymeans supplies to either or both the reformer and the oxygen electrodethe second oxygen-containing gas. As a result, water and soot containedin the combustion gas are not supplied to either or both the fuelelectrode and the oxygen electrode. Therefore, in accordance with thepresent invention, the fuel and oxygen electrodes are prevented fromundergoing deterioration by water and soot.

In addition, the second heat exchange means effects heat exchangebetween the combustion gas and the second oxygen-containing gas, wherebythe second oxygen-containing gas is heated. And, the oxygen-containinggas supply means supplies to either or both the reformer and the oxygenelectrode the second oxygen-containing gas thus heated. Therefore, itbecomes possible to raise the temperature of the electrolyte by makinguse of the heat held in the partial oxidation gas, the heat associatedwith the electrode reaction and the heat held in the secondoxygen-containing gas. Therefore, the time taken for the solidelectrolyte fuel cell to reach its operating temperature is reducedstill further. Accordingly, the present invention is able to reduce thestartup phase of the solid electrolyte fuel cell to a still furtherextent.

EFFECTS OF INVENTION

In accordance with the first invention, a supply of partial oxidationgas is provided to the fuel electrode, thereby making it possible toheat not only the fuel electrode but also the electrolyte by the use ofthe heat held in the partial oxidation gas. When the temperature of theelectrolyte rises to a predetermined degree, an electrode reaction iscaused to take place in the fuel electrode, the oxygen electrode and theelectrolyte by the use of hydrogen contained in the partial oxidationgas, thereby making it possible to start generating electrical power.Accordingly, it is possible to start the generation of electricity atthe predetermined temperature lower than the operating temperature ofthe solid electrolyte fuel cell.

Additionally, the electrode reaction accompanies the generation of heat.Therefore, the temperature of the electrolyte is increased by makingutilization of both the heat held in the partial oxidation gas and theheat associated with the electrode reaction. Therefore, the time takenfor the solid electrolyte fuel cell to reach its operating temperatureis reduced, and it becomes possible to reduce the startup phase of thesolid electrolyte fuel cell.

In accordance with the second invention, during the startup operation asupply of partial oxidation gas is provided to the fuel electrode,thereby making it possible to heat not only the fuel electrode but alsothe electrolyte by the use of the heat held in the partial oxidationgas. When the temperature of the electrolyte rises to a predetermineddegree, an electrode reaction is caused to take place in the fuelelectrode, the oxygen electrode and the electrolyte by the use ofhydrogen contained in the partial oxidation gas, thereby making itpossible to start generating electrical power. Accordingly, it ispossible to start the generation of electricity at the predeterminedtemperature lower than the operating temperature of the solidelectrolyte fuel cell.

Additionally, the electrode reaction accompanies the generation of heat.Therefore, the temperature of the electrolyte is increased by makingutilization of both the heat held in the partial oxidation gas and theheat associated with the electrode reaction. Therefore, the time takenfor the solid electrolyte fuel cell to reach its operating temperatureis reduced, and it becomes possible to reduce the startup phase of thesolid electrolyte fuel cell.

In addition to the above, during the normal operation, the reformerconverts hydrocarbons with a carbon number equal to or greater than 2into methane, in other words the fuel gas being supplied to the fuelelectrode does not contain hydrocarbons having a carbon number equal toor greater than 2. Therefore, even when the supply amount of water tothe fuel electrode is small, there are few possibilities that carbon maydeposit on the fuel electrode. Consequently, it is possible to preventthe occurrence of carbon deposition on the fuel electrode of the solidelectrolyte fuel cell.

In addition, during the normal operation, it is possible to convert thefuel gas into a reformed gas which contains hydrogen under the presenceof water in the fuel electrode of the solid electrolyte fuel cell.Therefore, it is possible to use such a reformed gas as thehydrogen-containing gas.

In accordance with the third invention, the first heat exchange meansoperates to effect heat exchange of the source gas and theoxygen-containing gas prior to their entry into the reformer with thepartial oxidation gas discharged out of the reformer, whereby thesematerial and oxygen-containing gases are heated by the heat held in thepartial oxidation gas. This therefore prevents the material andoxygen-containing gases from cooling the catalytic part of the reformer,and it becomes possible to cause the aforesaid partial oxidationreaction to take place actively in the reformer.

In accordance with the fourth invention, the first combustion gas supplymeans provides a supply of combustion gas to the reformer during thestartup phase of the reformer, whereby the reformer is heated with theheat held in the combustion gas. This arrangement makes it possible toincrease the temperature of the reformer up to the predetermined degree,and a partial oxidation reaction starts in the reformer. Accordingly,the reformer is activated.

In accordance with the fifth invention, the second combustion gas supplymeans provides a supply of combustion gas to the oxygen electrode beforean electrode reaction starts taking place and, as a result, not only theoxygen electrode but also the electrolyte is heated with the heat heldin the combustion gas. Accordingly, the electrolyte is heated with theheat held in the partial oxidation gas, the heat associated with theelectrode reaction and the heat held in the combustion gas. Therefore,the time taken for the solid electrolyte fuel cell to reach itsoperating temperature is reduced further, and it becomes possible toreduce the startup phase of the solid electrolyte fuel cell to a furtherextent.

In accordance with the sixth invention, the second heat exchange meanseffects heat exchange between the combustion gas and the secondoxygen-containing gas and, in addition, the oxygen-containing gas supplymeans supplies to either or both the reformer and the oxygen electrodethe second oxygen-containing gas. As a result, water and soot containedin the combustion gas are not supplied to either or both the fuelelectrode and the oxygen electrode. Therefore, the fuel and oxygenelectrodes are prevented from undergoing deterioration by water andsoot.

In addition, the second heat exchange means effects heat exchangebetween the combustion gas and the second oxygen-containing gas, wherebythe second oxygen-containing gas is heated. And, the oxygen-containinggas supply means supplies to either or both the reformer and the oxygenelectrode the second oxygen-containing gas thus heated. Therefore, itbecomes possible to raise the temperature of the electrolyte by makinguse of the heat held in the partial oxidation gas, the heat associatedwith the electrode reaction and the heat held in the secondoxygen-containing gas. Therefore, the time taken for the solidelectrolyte fuel cell to reach its operating temperature is reducedstill further, and it becomes possible to reduce the startup phase ofthe solid electrolyte fuel cell to a still further extent.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating in outline an arrangement of a fuelcell electrical power generation system according to an embodiment ofthe present invention;

FIG. 2 is a diagram illustrating in outline an arrangement of a fuelcell electrical power generation system according to another embodimentof the present invention; and

FIG. 3 is a diagram illustrating in outline an arrangement of a fuelcell electrical power generation system according to still anotherembodiment of the present invention.

BEST MODE FOR CARRYING OUT INVENTION Embodiment 1

Hereafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the drawings.

Referring to FIG. 1, there is shown a fuel cell electrical powergeneration system (1) according to the present embodiment. The fuel cellelectrical power generation system (1) comprises: a desulfurizer (3); afirst startup burner (4); a prereformer (5); a self heat exchanger (6);a solid electrolyte fuel cell (7) of the internal reforming type(hereafter referred to as the fuel cell); a combustor (9); a heatexchanger (11); first to eighth flow paths (13, 14, 15, 16, 17, 18, 19,20), first and second electromagnetic valves (21, 22); first to thirdblowers (23, 24, 25), etc. A first combustion means, a reformer, a solidelectrolyte fuel cell, a first heat-exchange means, a first combustiongas supply means and a partial oxidation gas supply means of the presentinvention are constituted by the first startup burner (4), theprereformer (5), the fuel cell (7), the self heat exchanger (6), thefourth flow path (16) and the fifth flow path (17), respectively.

One end of the first flow path (13) (i.e., the right-hand end in FIG. 1)is connected to an entrance port (3 a) of the desulfurizer (3).

The first blower (23) is a device for supplying a town gas to thedesulfurizer (3) via the first flow path (13). The town gas is a gaswhich contains CH₄, C₂H₆, C₃H₈, and C₄H₁₀.

The town gas having flowed into the desulfurizer (3) is flowedtherethrough. The desulfurizer (3) adsorbs sulfur compounds contained inthe inflowing town gas. An exit port (3 b) of the desulfurizer (3) isconnected to one end of the second flow path (14) (i.e., the left-handend).

The town gas having flowed out of the desulfurizer (3) and air areflowed through the first startup burner (4) during the startup phase ofthe prereformer (5) which will be described later. The town gas/air isburned in the first startup burner (4). The startup phase of theprereformer (5) is the time period until the time when the temperatureof the prereformer (5) rises to 400 degrees Centigrade. A first entranceport (4 a) of the first startup burner (4) is connected to the other endof the second flow path (14) (the right-hand end); a second entranceport (4 b) of the first startup burner (4) is connected to one end ofthe third flow path (15); and an exit port (4 c) of the first startupburner (4) is connected to one end of the fourth flow path (16).

The other end of the fourth flow path (16) is connected to an entranceport (5 a) of the prereformer (5).

One end of the fifth flow path (17) is connected to an exit port (5 b)of the prereformer (5), and the other end of the fifth flow path (17) isconnected to an entrance port (39 a) of a fuel chamber (39) of the fuelcell (7).

In the self heat exchanger (6), the fourth flow path (16) and the fifthflow path (17) extend parallel each other. And the self heat exchanger(6) effects heat exchange between the gas flowing through the fourthflow path (16) and the gas flowing through the fifth flow path (17).

During the startup phase of the fuel cell (7), the town gas/air etceterahaving being flowed through the desulfurizer (3) is flowed through theprereformer (5). The prereformer (5) generates a partial oxidation gaswhich contains carbon monoxide and hydrogen which are formed by partialoxidation of hydrocarbons contained in the town gas. The startup phaseof the fuel cell (7) is the time period until the time when thetemperature of the fuel cell (7) rises to 700-1000 degrees Centigrade.

In addition, the prereformer (5) is configured so as to operate asfollows. A source gas, i.e., a mixture of the town gas flowed throughthe desulfurizer (3) and a fuel re-circulation gas, is flowed throughthe prereformer (5) during the normal operation phase of the fuel cellelectrical power generation system (1). The prereformer (5) does notreform CH₄ present in the source gas, but it does convert hydrocarbons(such as C₂H₆, C₃H₈, C₄H₁₀, etcetera) contained in the source gas andhaving a carbon number equal to or greater than 2, into CH₄. The normaloperation phase of the fuel cell electrical power generation system (1)is the time period after the temperature of the fuel cell (7) rises to700-1000 degrees Centigrade.

The prereformer (5) is provided with a pipe which has a hollow part inwhich is disposed a catalytic part. The catalytic part is formed of aprecious metal catalyst, such as Ru, Rh, etcetera. Additionally, thecatalytic part has the property to adsorb sulfur compounds present inthe gas. Here, the amount of precious metal catalyst forming thecatalytic part should be set to a value minimum-required for adsorbingsulfides present in the gas which have not been adsorbed in thedesulfurizer (3) for a period from the time the fuel cell (7) is firstactivated until the time when the life of the fuel cell (7) isexhausted.

The fuel cell (7) is made up of: an air electrode (31) formed of (La,Ca) MnO₃; an electrolyte (33) formed of YSZ; a fuel electrode (35)formed of Ni-YSZ; an air chamber (37); a fuel chamber (39), externalcircuits (not shown), etcetera. The electrolyte (33) is impermeable togases and electrons but is permeable to only ions. The fuel electrode(35) is disposed on one surface of the electrolyte (33) (the left-handsurface), and the air electrode (31) is disposed on the other side ofthe electrolyte (33) (the right-hand surface). And the fuel chamber (39)and the air chamber (37) are defined on the fuel electrode's (35) sideand on the air electrode's (31) side, respectively, with the electrolyte(33) as a partition wall lying therebetween. The fuel electrode (35) andthe air electrode (31) are connected together via an external circuit(not shown). The operating temperature of the fuel cell (7) is 700-1000degrees Centigrade. The oxygen electrode, referred to in the presentinvention, is implemented by the air electrode (31).

An entrance port (37 a) of the air chamber (37) is connected to one endof the sixth flow path (18) (the upper end). And when the firstelectromagnetic valve (21) is placed in the open state, a supply of airis provided to the air chamber (37).

During the startup phase of the fuel cell (7), a partial oxidation gaswhich contains CO and H₂ flows out of the prereformer (5), and issupplied to the fuel chamber (39).

In addition, during the normal operation of the fuel cell electricalpower generation system (1), a CH₄-containing fuel gas flows out of theprereformer (5), and is supplied to the fuel chamber (39).

A re-circulation port (39 b) of the fuel chamber (39) is connected to ahalfway part of the second flow path (14) via the seventh flow path(19). And a CO and H₂-containing fuel re-circulation gas discharged fromthe fuel chamber (39) is delivered to the second flow path (14) by thesecond blower (24). The fuel re-circulation gas flows into the secondflow path (14), and is mixed with the town gas flowed through thedesulfurizer (3).

The combustor (9) is connected to the air and fuel chambers (37) and(39) of the fuel cell (7). And the combustor (9) burns a CO andH₂-containing exhaust gas discharged from the fuel chamber (39) and anexhaust gas discharged from the air chamber (37).

The eighth flow path (20) is a flow path through which the exhaust gasburned in the combustor (9) flows. One end of the eighth flow path (20)(the left-hand end) is connected to the combustor (9), and the other endof the eighth flow path (20) (the right-hand end) is connected to anexhaust gas discharge port (not shown).

The third blower (25) supplies air to either or both the first startupburner (4) and the air chamber (37) of the fuel cell (7) via the thirdflow path (15).

In the heat exchanger (11), the third flow path (15) and the eighth flowpath (20) extend parallel each other. The heat exchanger (11) isconfigured to effect heat exchange between the air flowing through thethird flow path (15) and the exhaust gas flowing through the eighth flowpath (20).

The second electromagnetic valve (22) is disposed between the junctionpoint of the third flow path (15) and the sixth flow path (18) and thefirst startup burner (4) in the third flow path (15).

Here, how the fuel cell electrical power generation system (1) operatesis described below.

Startup of Prereformer

First, the prereformer (5) is started up.

During the startup phase of the prereformer (5), the firstelectromagnetic valve (21) is placed in the closed state, while thesecond electromagnetic valve (22) is placed in the open state. The firststartup burner (4) is in operation.

A town gas flows into the desulfurizer (3) via the first flow path (13).And the town gas having entered the inside of the desulfurizer (3) flowstherethrough, and sulfur compounds contained in the town gas areremoved.

Then, the sulfide-free town gas leaves the desulfurizer (3), and flowsinto the first startup burner (4) via the second flow path (14).

On the other hand, a stream of air flows into the heat exchanger (11)via the third flow path (15). The heat exchanger (11) effects heatexchange between the air and the exhaust gas burned in the combustor(9). Thereby, the air is heated.

The air thus heated flows out of the heat exchanger (11), and enters theinside of the first startup burner (4) via the third flow path (15).

And the town gas and the air which have flowed into the first startupburner (4) are burned in the first startup burner (4).

A combustion gas, generated as a result of the burning of the town gasand the air in the first startup burner (4), flows out of the firststartup burner (4), and then enters the inside of the self-heatexchanger (6) via the fourth flow path (16). And the self-heat exchanger(6) effects heat exchange between the combustion gas flowing through thefourth flow path (16) and the combustion gas flowing through the fifthflow path (17).

After flowing through the self-heat exchanger (6), the combustion gasflows into the prereformer (5). And the combustion gas flows through theprereformer (5), as a result of which the catalytic part of theprereformer (5) is preheated. Preheating of the catalytic part ofprereformer (5) is carried out until the time when the temperature ofthe catalytic part rises to 400 degrees Centigrade. The reason for suchpreheating of the catalytic part of the prereformer (5) up to 400degrees Centigrade is that when the temperature of the catalytic partincreases up to 400 degrees Centigrade it becomes possible to start apartial oxidation reaction (described later) in the prereformer (5).

After flowing through the prereformer (5), the combustion gas leaves theprereformer (5), and flows into the fuel chamber (39) of the fuel cell(7) via the fifth flow path (17).

The combustion gas having entered inside of the fuel chamber (39) passesthrough the combustor (9) and then through the eighth flow path (20),and is discharged from the discharge port.

Preheating of Fuel Cell

Next, preheating of the fuel cell (7) is carried out.

Here, the first startup burner (4) is stopped when the temperature ofthe catalytic part of prereformer (5) rises to 400 degrees Centigrade.At this time, the first electromagnetic valve (21) which is placed inthe closed state during the startup phase of the prereformer (5) is nowplaced in the open state.

First, at the junction point of the second flow path (14) and theseventh flow path (19), a town gas is mixed with a fuel re-circulationgas which contains CO and H₂. A source gas which is a mixture of thetown gas and the fuel re-circulation gas flows into the first startupburner (4) in the stopped state via the second flow path (14).

On the other hand, the air flows out of the heat exchanger (11), flowsin the third flow path (15), and arrives at the junction point of thethird flow path (15) and the sixth flow path (18). And at the junctionpoint, the air flow branches off to the third flow path (15) and to thesixth flow path (18).

The air having flowed into the third flow path (15) passes therethroughand enters the inside of the first startup burner (4) in the stoppedstate.

The source gas/air having entered the inside of the first startup burner(4) leaves there, and then enters the inside of the self heat exchanger(6) via the fourth flow path (16). And the self heat exchanger (6)effects heat exchange between the source gas flowing through the fourthflow path (16) and the partial oxidation gas flowing through the fifthflow path (17). Thereby, the source gas passing through the fourth flowpath (16) is heated.

The source gas thus heated flows into the prereformer (5). And when thesource gas flows through the catalytic part of the prereformer (5), apartial oxidation reaction, in which hydrocarbon contained in the sourcegas reacts with oxygen to form carbon monoxide and hydrogen, takesplace.

The aforesaid partial oxidation reaction, which is an exothermicreaction, is expressed as follows.C_(n)H_(2n+2) +n/2O₂ →nCO+(n+1)H₂  (1)

That is, in the catalytic part of the prereformer (5), the reactionexpressed by the reaction formula (1) takes place, and carbon monoxideand hydrogen are generated from hydrocarbon and oxygen.

From the reaction formula (1), it can be considered that two differentreactions take place at the same time, i.e., a forward reaction from theleft side to the right side and a backward reaction from the right sideto the left side. However, the forward reaction is more than thebackward reaction. Accordingly, it can be considered that the forwardreaction takes place.

Incidentally, when the town gas is flowed through the desulfurizer (3),not all the sulfur compounds contained in the town gas are removed bythe desulfurizer (3). Here, the catalytic part of the prereformer (5)has the property to adsorb sulfur compounds present in the gas.Therefore, the sulfur compounds still lingering in the source gas areremoved when flowed through the prereformer (5).

Next, a partial oxidation gas which contains CO and H₂ generated as aresult of the flowing of the source gas through the prereformer (5)flows into the fuel chamber (39) of the fuel cell (7) via the fifth flowpath (17). Here, since the reaction expressed by the formula (1) is anexothermic reaction, the partial oxidation gas holds heat. Therefore,when the partial oxidation gas flows through the fuel chamber (39), notonly the fuel electrode (35) but also the electrolyte (33) is preheated.

On the other hand, the air having flowed into the sixth flow path (18)passes therethrough and enters the inside of the air chamber (37) of thefuel cell (7). And the air flows through the air chamber (37), therebypreheating not only the air electrode (31) but also the electrolyte(33).

Preheating of the fuel cell (7) continues until the time when thetemperature of the fuel cell (7) rises to 500 degrees Centigrade. Here,since ions are allowed to move in the electrolyte (33) when thetemperature of the fuel cell (7) rises to 500 degrees Centigrade, thisenables the fuel cell (7) to generate electrical power.

Next, the CO and H₂-containing fuel re-circulation gas discharged fromthe fuel chamber (39) flows into the second flow path (14) via theseventh flow path (19). And the fuel re-circulation gas is mixed withthe town gas at the junction point of the second flow path (14) and theseventh flow path (19).

In addition, the CO and H₂-containing exhaust gas discharged from thefuel chamber (39) and the exhaust gas discharged from the air chamber(37) flow into the combustor (9) and are burned there.

Such combustion is expressed by the following reaction formulas.CO+½O₂→CO₂  (2)H₂+½O₂→H₂O  (3)

The exhaust gas thus burned flows into the heat exchanger (11) via theeighth flow path (20), and exchanges heat with the air flowing throughthe third flow path (15).

After flowing through the heat exchanger (11), the exhaust gas passesthrough the eighth flow path (20), and is discharged from a dischargeport.

Start of Electrical Power Generation

Next, while continuously preheating the fuel cell (7), the generation ofelectrical power is started. The startup operation as referred to in thepresent invention corresponds to the operation during the preheating ofthe fuel cell (7) and to the operation at the time when the fuel cell(7) starts generating electrical power.

Here, when the temperature of the fuel cell (7) rises to 500 degreesCentigrade, the first startup burner (4) still remains in the stoppedstate. At this time, the first and second electromagnetic valves (21,22) are still in their open state.

The partial oxidation gas which contains CO and H₂ generated as a resultof the flowing of the source gas through the prereformer (5) flows intothe fuel chamber (39) of the fuel cell (7) via the fifth flow path (17).

On the other hand, the air flows into the air chamber (37) of the fuelcell (7) via the third and sixth flow paths (15, 18).

Next, how the fuel cell (7) operates is explained in detail.

First, a reaction, in which oxygen present in the air chamber (37) isdissociated at the interface between the air electrode (31) and theelectrolyte (33) and becomes oxygen ions, takes place.

The aforesaid reaction is expressed as follows.½O₂+2e ⁻→O²⁻  (4)

The oxygen ions move towards the fuel electrode (35) through theelectrolyte (33).

And a reaction, in which the oxygen ions react with carbon monoxide andhydrogen contained in the partial oxidation gas in the fuel chamber (39)to generate carbon dioxide and steam at the interface between the fuelelectrode (35) and the electrolyte (33), takes place.

The aforesaid reaction is expressed as follows.CO+O²⁻→CO₂+2e ⁻  (5)H₂+O²⁻→H₂O+2e ⁻  (6)

At this time, electrons emitted from O²⁻ flow into an external circuitfrom the fuel electrode (35). And electric energy is taken out in theexternal circuit and the generation of electrical power starts.

Further, electrons flow into the air electrode (31) from the externalcircuit, and, as shown in the reaction formula (4), react with oxygen inthe air chamber (37) at the interface between the air electrode (31) andthe electrolyte (33), and become oxygen ions.

Preheating of the fuel cell (7) is carried out with the heat held in thepartial oxidation gas, the heat held in the air and the heat generatedat the time of the generation of electrical power. The fuel cell (7) iscontinuously preheated until the time when the temperature of the fuelcell (7) rises to 700-1000 degrees Centigrade (the operatingtemperature). Here, since ions are allowed to move smoothly in theelectrolyte (33) when the temperature of the fuel cell (7) rises to 700degrees Centigrade, the fuel cell electrical power generation systembecomes ready to perform its normal operation (described later).

Next, the fuel re-circulation gas which contains CO₂, H₂O, CO and H₂ isdischarged from the fuel chamber (39) and flows into the second flowpath (14) via the seventh flow path (19). And the fuel re-circulationgas is mixed with the town gas at the junction point of the second flowpath (14) and the seventh flow path (19).

Normal Operation of Fuel Cell Electrical Power Generation System

Next, the fuel cell electrical power generation system (1) carries outits normal operation.

The first startup burner (4) still remains in the stopped state when thetemperature of the fuel cell (7) rises to 700-1000 degrees Centigrade.At this time, the first electromagnetic valve (21) is still in the openstate. On the other hand, the second electromagnetic valve (22) isplaced in the closed state.

A source gas which is a mixture of the town gas and the fuelre-circulation gas enters the inside of the prereformer (5) via thesecond and fourth flow paths (14, 16).

Next, how the prereformer (5) operates is described in detail.

The source gas flows through the catalytic part of the prereformer (5),wherein in the catalytic part a methanation reaction, in whichhydrocarbons having a carbon number equal to or greater than 2 reactwith hydrogen to form methane, takes place actively while a steamreforming reaction, in which hydrocarbons having a carbon number equalto or greater than 2 react with steam to form hydrogen and carbonmonoxide, takes place somewhat. The methanation reaction takes placethroughout the catalytic part of prereformer (5). On the other hand, thesteam reforming reaction takes place mainly at an area of the catalyticpart on the side of the entrance port (5 a) of the prereformer (5).

The methanation reaction, which is an exothermic reaction, is expressedby the following reaction formula.C_(n)H_(2n+2)+(n−1)H₂ →nCH₄  (7)

Here, H₂ used in the methanation reaction includes H₂ generated in thesteam reforming reaction and H₂ contained in the fuel re-circulationgas.

The steam reforming reaction, which is an endothermal reaction, isexpressed by the following reaction formula.C_(n)H_(2n+2) +nH₂O→nCO+(2n+1)H₂  (8)

That is, in the catalytic part of the prereformer (5), both the reactionexpressed by the reaction formula (7) and the reaction expressed by thereaction formula (8) take place, and methane, carbon monoxide andhydrogen are generated from hydrocarbons with a carbon number equal toor greater than 2.

The fuel gas which contains CH₄ and H₂O generated as a result of theflowing of the source gas through the prereformer (5) enters the insideof the fuel chamber (39) of the fuel cell (7) via the fifth flow path(17).

On the other hand, air enters the inside of the air chamber (37) of thefuel cell (7) via the third and sixth flow paths (15, 18).

Next, how the fuel cell (7) operates is described below.

In the fuel chamber (39), a steam reforming reaction, in which methanereacts with steam to form carbon monoxide and hydrogen, takes place bythe catalytic action of Ni contained in the fuel electrode (35).

Such a steam reforming reaction, which is an endothermal reaction, isexpressed by the following reaction formula.CH₄+H₂O→CO+3H₂  (9)

Thereafter, in the fuel cell (7), the same electrode reaction as theabove takes place. Thereby, electrical power is generated.

In the present embodiment, it is arranged such that during the startupphase of the fuel cell (7) the partial oxidation gas is supplied to thefuel chamber (39) via the fourth flow path (16). As a result of sucharrangement, not only the fuel electrode (35) but also the electrolyte(33) is preheated by making use of the heat held in the partialoxidation gas. And when the temperature of the electrolyte (33) rises to500 degrees Centigrade, an electrode reaction is caused to take place inthe fuel cell (7) by the use of CO and H₂ contained in the partialoxidation gas, thereby making it possible to start the generation ofelectrical power. To sum up, it is possible for the fuel cell (7) tostart generating electricity at a temperature of 500 degrees Centigradelower than the operating temperature of the fuel cell (7).

The electrode reaction accompanies the generation of heat. Thistherefore makes it possible to preheat the electrolyte (33) by the heatheld in the partial oxidation gas and the heat associated with theelectrode reaction. Therefore, it becomes possible to reduce the lengthof time until the temperature of the fuel cell (7) reaches its operatingtemperature. Consequently, the startup phase of the fuel cell (7) isreduced.

In addition, during the startup phase of the fuel cell (7), the selfheat exchanger (6) effects heat exchange between the source gas/airprior to entry into the prereformer (5) and the partial oxidation gasdischarged from the prereformer (5), whereby the source gas/air isheated by the heat held in the partial oxidation gas. As the result ofthis, the catalytic part of the prereformer (5) is prevented from beingcooled by the source gas/air. Therefore, in the prereformer (5), theaforesaid partial oxidation reaction is caused to take place actively.

Furthermore, the combustion gas discharged from the first startup burner(4) is supplied to the prereformer (5) via the fourth flow path (16)during the startup phase of the prereformer (5), so that the prereformer(5) is preheated by the heat held in the combustion gas. Therefore, itis possible to increase the temperature of the prereformer (5) to 400degrees Centigrade, thereby allowing a partial oxidation reaction totake place in the prereformer (5). Consequently, the present embodimentenables the prereformer (5) to start operating.

During the normal operation of the fuel cell electrical power generationsystem (1), the prereformer (5) reforms hydrocarbons having a carbonnumber equal to or greater than 2 (i.e., C₂H₆, C₃H₈, C₄H₁₀ etcetera)present in the source gas into CH₄. Therefore, the fuel gas which issupplied to the fuel chamber (39) does not contain hydrocarbons whosecarbon number is 2 or greater. Therefore, the hydrocarbon contained inthe fuel gas is only CH₄, so that even when the supply amount of waterto the fuel chamber (39) is small, there are few possibilities thatcarbon may deposit in the fuel chamber (39): Consequently, in the normaloperation of the fuel cell electrical power generation system (1), it ispossible to prevent the occurrence of carbon deposition in the fuelchamber (39) of the fuel cell (7).

Embodiment 2

In a fuel cell electrical power generation system (1) according to asecond embodiment of the present invention, a combustion gas is suppliedto the air chamber before starting generating electrical power.

Referring to FIG. 2, the fuel cell electrical power generation system(1) of the present embodiment includes: a desulfurizer (3); a secondstartup burner (8); a prereformer (5); a fuel cell (7); a combustor (9);a heat exchanger (11); ninth to nineteenth flow paths (43, 45, 47, 49,51, 53, 55, 57, 59, 61, 62); third to sixth electromagnetic valves (63,65, 67, 69); a directional control valve (71); first to third blowers(23, 24, 25) etcetera. And a second combustion means of the presentinvention is constituted by the second startup burner (8), and a secondcombustion gas supply means of the present invention is constituted bythe sixteenth and seventeenth flow paths (57, 59).

One end of the ninth flow path (43) (the right-hand end in FIG. 2) isconnected to an entrance port (3 a) of the desulfurizer (3).

One end of the tenth flow path (45) (the left-hand end) is connected toan exit port (3 b) of the desulfurizer (3), and the other end of thetenth flow path (45) (the right-hand end) is connected to an entranceport (5 a) of the prereformer (5).

One end of the eleventh flow path (47) is connected to between the exitport (3 b) of the desulfurizer (3) and the third electromagnetic valve(63) in the tenth flow path (45). The other end of the eleventh flowpath (47) is connected to a first entrance port (8 a) of the secondstartup burner (8). One end of the twelfth flow path (49) is connectedto a second entrance port (8 b) of the second startup burner (8).

One end of the thirteenth flow path (51) is connected to are-circulation port (39 b) of the fuel chamber (39). The other end ofthe thirteenth flow path (51) is connected to between the junction pointof the tenth flow path (45) and the fourteenth flow path (53) and thethird electromagnetic valve (63) in the tenth flow path (45).

One end of the fourteenth flow path (53) (the lower end) is connected toa halfway part of the sixteenth flow path (57). The other end of thefourteenth flow path (53) (the upper end) is connected to between thejunction point of the tenth flow path (45) and the thirteenth flow path(51) and the junction point of the tenth flow path (45) and thefifteenth flow path (55) in the tenth flow path (45).

One end of the fifteenth flow path (55) is connected to between the heatexchanger (11) and the directional control valve (71) in the twelfthflow path (49). The other end of the fifteenth flow path (55) isconnected to between the junction point of the tenth flow path (45) andthe fourteenth flow path (53) and the entrance port (5 a) of theprereformer (5) in the tenth flow path (45).

One end of the sixteenth flow path (57) (the left-hand end) is connectedto an exit port (8 c) of the second startup burner (8). The other end ofthe sixteenth flow path (57) (the right-hand end) is connected to ahalfway part of the seventeenth flow path (59).

One end of the seventeenth flow path (59) (the lower end) is connectedto the directional control valve (71). The other end of the seventeenthflow path (59) (the upper end) is connected to an entrance port (37 a)of the air chamber (37).

One end of the eighteenth flow path (61) (the left-hand end) isconnected to the combustor (9). The other end of the eighteenth flowpath (61) (the right-hand end) is connected to an exhaust gas dischargeport (not shown).

One end of the nineteenth flow path (62) (the left-hand end) isconnected to the exit port (5 b) of the prereformer (5). The other endof the nineteenth flow path (62) (the right-hand end) is connected to anentrance port (39 a) of the fuel chamber (39) of the fuel cell (7).

In the inside of the heat exchanger (11), the twelfth flow path (49) andthe eighteenth flow path (61) extend parallel each other.

The fourth electromagnetic valve (65) is disposed midway along theeleventh flow path (47); the fifth electromagnetic valve (67) isdisposed midway along the fourteenth flow path (53); and the sixthelectromagnetic valve (69) is disposed midway along the fifteenth flowpath (55).

The directional control valve (71) is configured such that the airflowing through the twelfth flow path (49) is directed to flow througheither the twelfth flow path (49) or the seventeenth flow path (59).

Here, how the fuel cell electrical power generation system (1) operatesis described.

Startup of Prereformer and Preheating of Air Electrode

First, the prereformer (5) is started up and the air electrode (31) ispreheated.

Here, during the startup of the prereformer (5) and the preheating ofthe air electrode (31), the fourth and fifth electromagnetic valves (65,67) are placed in the open state, while the third and sixthelectromagnetic valves (63, 69) are placed in the closed state. Thedirectional control valve (71) permits the air to flow into the twelfthflow path (49). In addition, the second startup burner (8) is inoperation.

The sulfide-free town gas leaves the desulfurizer (3), and flows intothe second startup burner (8) via the tenth and eleventh flow paths (45,47).

On the other hand, air enters the inside of the heat exchanger (11) viathe twelfth flow path (49). The heat exchanger (11) effects heatexchange between the air and the exhaust gas burned in the combustor(9). Thereby, the air is heated.

The air thus heated flows into the second startup burner (8) by way ofthe twelfth flow path (49).

And the town gas/air having flowed into the second startup burner (8) isburned there.

A combustion gas generated as a result of the burning of the towngas/air in the second startup burner (8) flows out of the second startupburner (8), flows in the sixteenth flow path (57), and arrives at thejunction point of the fourteenth flow path (53) and the sixteenth flowpath (57). And at that junction point, the combustion gas flow branchesoff to the fourteenth flow path (53) and to the sixteenth flow path(57).

The combustion gas having flowed into the fourteenth flow path (53)enters the inside of the prereformer (5) via the fourteenth and tenthflow paths (53, 45). And the combustion gas flows through theprereformer (5), thereby preheating the catalytic part of theprereformer (5). Preheating of the catalytic part of the prereformer (5)is continuously carried out until the time when the temperature of thecatalytic part rises to 400 degrees Centigrade.

After flowing through the prereformer (5), the combustion gas leavesthere, and flows into the fuel chamber (39) via the fifth flow path(17).

On the other hand, the combustion gas having flowed into the sixteenthflow path (57) enters the inside of the air chamber (37) via thesixteenth and seventeenth flow paths (57, 59). And the combustion gasflows through the air chamber (37), thereby preheating not only the airelectrode (31) but also the electrolyte (33).

Both the combustion gas flowed through the air chamber (37) and thecombustion gas flowed through the fuel chamber (39) flow into thecombustor (9).

Preheating of Fuel Cell

Next, preheating of the fuel cell (7) is carried out.

Here, when the temperature of the catalytic part of the prereformer (5)rises to 400 degrees Centigrade, the third, fourth and sixthelectromagnetic valves (63, 65, 69) are placed in the open state, whilethe fifth electromagnetic valve (67) is placed in the closed state. Atthis time, the second startup burner (8) operates and the directionalcontrol valve (71) permits air to flow into the twelfth flow path (49).

First, the town gas having flowed out of the desulfurizer (3) flows inthe tenth flow path (45) and arrives at the junction point of the tenthflow path (45) and the eleventh flow path (47). And at the junctionpoint, the town gas flow branches off to the tenth flow path (45) and tothe eleventh flow path (47).

The town gas having flowed into the tenth flow path (45) flows thereinand arrives at the junction point of the tenth flow path (45) and thethirteenth flow path (51). And the town gas is mixed with a fuelre-circulation gas at the junction point.

A source gas, i.e., a mixture of the town gas and the fuelre-circulation gas, flows in the tenth flow path (45) and arrives at thejunction point of the tenth flow path (45) and the fifteenth flow path(55). And the source gas is mixed with the air flowed through thefifteenth flow path (55) at the junction point.

The source gas/air enters the inside of the prereformer (5) via thetenth flow path (45). And by the flowing of the source gas/air throughthe catalytic part of the prereformer (5), the above-mentioned partialoxidation reaction takes place.

A partial oxidation gas generated as a result of the flowing of thesource gas/air through the prereformer (5) flows into the fuel chamber(39) of the fuel cell (7) via the nineteenth flow path (62). And by theflowing of the partial oxidation gas through the fuel chamber (39), notonly the fuel electrode (35) but also the electrolyte (33) is preheated.

On the other hand, the town gas having flowed into the eleventh flowpath (47) enters the inside of the second startup burner (8) via theeleventh flow path (47).

In addition, the air flows in the twelfth flow path (49) and arrives atthe junction point of the twelfth flow path (49) and the fifteenth flowpath (55). And at the junction point, the air flow branches off to thetwelfth flow path (49) and to the fifteenth flow path (55).

The air having flowed into the twelfth flow path (49) enters the insideof the second startup burner (8) via the twelfth flow path (49).

A combustion gas generated as a result of the burning of the towngas/air in the second startup burner (8) leaves the second startupburner (8), and flows into the air chamber (37) via the sixteenth andseventeenth flow paths (57, 59). And by the flowing of the combustiongas through the air chamber (37), not only the air electrode (31) butalso the electrolyte (33) is preheated.

The fuel cell (7) is continuously preheated until the time when thetemperature of the fuel cell (7) rises to 500 degrees Centigrade.

Start of Electrical Power Generation

Next, while continuously preheating the fuel cell (7), the generation ofelectrical power starts.

Here, the second startup burner (8) is stopped when the temperature ofthe fuel cell (7) rises to 500 degrees Centigrade. In addition, at thistime, the third and sixth electromagnetic valves (63, 69) are placed inthe open state, while the fourth and fifth electromagnetic valves (65,67) are placed in the closed state. Furthermore, the directional controlvalve (71) permits air to flow into the seventeenth flow path (59).

A source gas which is a mixture of the town gas and the fuelre-circulation gas flows in the tenth flow path (45) and arrives at thejunction point of the tenth flow path (45) and the fifteenth flow path(55). And the source gas is mixed with the air flowed through thefifteenth flow path (55) at the junction point.

The source gas/air enters the inside of the prereformer (5) via thetenth flow path (45). And by the flowing of the source gas/air throughthe catalytic part of the prereformer (5), a partial oxidation reactionis caused to take place.

A partial oxidation gas which contains CO and H₂ generated as a resultof the flowing of the source gas through the prereformer (5) flows intothe fuel chamber (39) via the nineteenth flow path (62).

On the other hand, air flows into the air chamber (37) via the twelfthand seventeenth flow paths (49, 59).

Thereafter, in the fuel cell (7), the same electrode reaction as theabove takes place. Thereby, electrical power is generated.

The fuel cell (7) is preheated by making use of the heat held in thepartial oxidation gas, the heat held in the air and the heat generatedat the time of the generation of electrical power. The fuel cell (7) iscontinuously preheated until the time when the temperature of the fuelcell (7) rises to 700-1000 degrees Centigrade.

The start of an electrode reaction as referred to in the presentinvention corresponds to the time when the generation of electricalpower starts.

Normal Operation of Fuel Cell Electrical Power Generation System

Next, the fuel cell electrical power generation system (1) performs itsnormal operation.

Here, the second startup burner (8) still remains in the stopped statewhen the temperature of the fuel cell (7) rises to 700-1000 degreesCentigrade. At this time, the third electromagnetic valve (63) is placedin the open state, while the fourth, fifth and sixth electromagneticvalves (65, 67, 69) are placed in the closed state. The directionalcontrol valve (71) permits air to flow into the seventeenth flow path(59).

A source gas which is a mixture of the town gas and the fuelre-circulation gas flows into the prereformer (5) via the tenth flowpath (45). And in the prereformer (5), the same methanation reaction asthe above takes place.

A fuel gas which contains CH₄ and H₂O generated as a result of theflowing of the source gas through the prereformer (5) flows into thefuel chamber (39) via the nineteenth flow path (62).

On the other hand, air flows into the air chamber (37) via the twelfthand seventeenth flow paths (49, 59).

Thereafter, in the fuel cell (7), the same steam reforming and electrodereactions as the above take place. Thereby, electrical power isgenerated.

In the present embodiment, before starting generating electrical power,a combustion gas is supplied, via the sixteenth and seventeenth flowpaths (57, 59), to the air chamber (37), whereby not only the airelectrode (31) but also the electrolyte (33) is heated by making use ofthe heat held in the combustion gas. Therefore, the electrolyte (33) isheated by making use of the heat held in the partial oxidation gas, theheat associated with the electrode reaction and the heat held in thecombustion gas. Consequently, the length of time until the fuel cell (7)reaches its operating temperature is reduced further. Therefore, thelength of time required to activate the fuel cell (7) is reduced to afurther extent.

Embodiment 3

A fuel cell electrical power generation system of the present embodimentis characterized in that air having undergone heat exchange with acombustion gas during the startup phase of the fuel cell is supplied tothe prereformer and to the air chamber.

Referring to FIG. 3, the fuel cell electrical power generation system(1) according to the present embodiment comprises: a desulfurizer (3); athird startup burner (12); a prereformer (5); a fuel cell (7), acombustor (9); first and second heat exchangers (93, 95); twentieth totwenty-ninth flow paths (73, 75, 77, 79, 81, 83, 85, 87, 89, 91);seventh to tenth electromagnetic valves (97, 99,101,103); first to thirdblowers (23, 24, 25) et cetera. A third combustion means of the presentinvention is constituted by the third startup burner (12); an oxygencontaining gas supply means of the present invention is constituted bythe twenty-first, twenty-fifth and twenty-seventh flow paths (75, 83,87); and a second heat exchange means of the present invention isconstituted by the first heat exchanger (93).

One end of the twentieth flow path (73) (the right-hand end in FIG. 3)is connected to an entrance port (3 a) of the desulfurizer (3).

One end of the twenty-first flow path (75) (the left-hand end) isconnected to an exit port (3 b) of the desulfurizer (3). The other endof the twenty-first flow path (75) (the right-hand end) is connected toan entrance port (5 a) of the prereformer (5).

One end of the twenty-second flow path (77) is connected to between theexit port (3 b) of the desulfurizer (3) and the seventh electromagneticvalve (97) in the twenty-first flow path (75). The other end of thetwenty-second flow path (77) is connected to a first entrance port (12a) of the third startup burner (12).

One end of the twenty-third flow path (79) is connected to a secondentrance port (12 b) of the third startup burner (12).

One end of the twenty-fourth flow path (81) is connected to are-circulation port (39 b) of the fuel chamber (39). The other end ofthe twenty-fourth flow path (81) is connected to between the junctionpoint of the twenty-first flow path (75) and the twenty-fifth flow path(83) and the seventh electromagnetic valve (97) in the twenty-first flowpath (75).

One end of the twenty-fifth flow path (83) is connected to between thesecond heat exchanger (95) and the tenth electromagnetic valve (103) inthe twenty-third flow path (79). The other end of the twenty-fifth flowpath (83) is connected to between the junction point of the twenty-firstflow path (75) and the twenty-fourth flow path (81) and the entranceport (5 a) of the prereformer (5) in the tenth flow path (45).

One end of the twenty-sixth flow path (85) (the left-hand end) isconnected to the exit port (5 b) of the prereformer (5). The other endof the twenty-sixth flow path (85) (the right-hand end) is connected toan entrance port (39 a) of the fuel chamber (39).

One end of the twenty-seventh flow path (87) is connected to between theninth electromagnetic valve (101) and the first heat exchanger (93) inthe twenty-fifth flow path (83). The other end of the twenty-seventhflow path (87) is connected to an entrance port (37 a) of the airchamber (37).

One end of the twenty-eighth flow path (89) is connected to an exit port(12 c) of the third startup burner (12). The other end of thetwenty-eighth flow path (89) is connected to a combustion gas dischargeport (not shown).

One end of the twenty-ninth flow path (91) (the left-hand end) isconnected to the combustor (9). The other end of the twenty-ninth flowpath (91) (the right-hand end) is connected to an exhaust gas dischargeport (not shown).

In the first heat exchanger (93), the twenty-fifth flow path (83) andthe twenty-eighth flow path (89) extend parallel each other.

In the second heat exchanger (95), the twenty-third flow path (79) andthe twenty-ninth flow path (91) extend parallel each other.

The eighth electromagnetic valve (99) is disposed midway along thetwenty-second flow path (77). The ninth electromagnetic valve (101) isdisposed between the junction point of the twenty-fifth flow path (83)and the twenty-seventh flow path (87) and the junction point of thetwenty-fifth flow path (83) and the twenty-first flow path (75) in thetwenty-fifth flow path (83).

Here, how the fuel cell electrical power generation system (1) operatesis described below.

Startup of Prereformer and Preheating of Air Electrode

First, the prereformer (5) is started up and the air electrode (31) ispreheated.

During the startup phase of the prereformer (5) and the preheating phaseof the air electrode (31), the eighth, ninth and tenth electromagneticvalves (99,101,103) are placed in the open state, while the seventhelectromagnetic valve (97) is placed in the closed state. The thirdstartup burner (12) is in operation.

A sulfide-free town gas flows out of the desulfurizer (3) and enters theinside of the third startup burner (12) via the twenty-first and secondflow paths (75, 77).

On the other hand, air flows into the second heat exchanger (95) via thetwenty-third flow path (79). And in the second heat exchanger (95) theair exchanges heat with the exhaust gas burned in the combustor (9).Thereby, the air is heated.

The air thus heated flows in the twenty-third flow path (79) and arrivesat the junction point of the twenty-third flow path (79) and thetwenty-fifth flow path (83). At the junction point, the air flowbranches off to the twenty-third flow path (79) and to the twenty-fifthflow path (83).

The air having flowed into the twenty-third flow path (79) flows thereinand enters the inside of the third startup burner (12).

On the other hand, the air having flowed into the twenty-fifth flow path(83) flows therein and enters the inside of the first heat exchanger(93).

The town gas/air having entered the inside of the third startup burner(12) is burned there.

A combustion gas generated as a result of the burning of the towngas/air in the third startup burner (12) flows out of the third startupburner (12), and enters the inside of the first heat exchanger (93) viathe twenty-eighth flow path (89). And the first heat exchanger (93)effects heat exchange between the air flowing through the twenty-fifthflow path (83) and the combustion gas flowing through the twenty-eighthflow path (89). Thereby, the air is heated.

The air thus heated flows in the twenty-fifth flow path (83) and arrivesat the junction point of the twenty-fifth flow path (83) and thetwenty-seventh flow path (87). And at the junction point, the air flowbranches off to the twenty-fifth flow path (83) and to the twentyseventh flow path (87).

The air having flowed into the twenty-fifth flow path (83) flows in thetwenty-fifth and first flow paths (83, 75) and enters the inside of theprereformer (5). By the flowing of the air through the prereformer (5),the catalytic part of the prereformer (5) is preheated. The catalyticpart of the prereformer (5) is preheated until the time when thetemperature of the catalytic part amounts rises to 400 degreesCentigrade.

After being flowed through the prereformer (5), the air flows out of theprereformer (5), and enters the inside of the fuel chamber (39) via thetwenty-sixth flow path (85).

On the other hand, the air having flowed into the twenty-seventh flowpath (87) flows therein and enters the inside of the air chamber (37).And by the flowing of the air through the air chamber (37), not only theair electrode (31) but also the electrolyte (33) is preheated.

A stream of air discharged from the air chamber (37) and another streamof air discharged from the fuel chamber (39) flow through the combustor(9) and then through the twenty-ninth flow path (91), and are dischargedfrom a discharge port.

On the other hand, the combustion gas flows out of the first heatexchanger (93), flows through the twenty-eighth flow path (89), and isdischarged from a discharge port.

Preheating of Fuel Cell

Next, preheating of the fuel cell (7) is carried out.

Here, when the temperature of the catalytic part of the prereformer (5)rises to 400 degrees Centigrade, all the electromagnetic valves (97,99,101,103) are placed in the open state. The third startup burner (12)is still in operation.

The town gas having flowed out of the desulfurizer (3) flows in thetwenty-first flow path (75) and arrives at the junction point of thetwenty-first flow path (75) and the twenty-second flow path (77). And atthe junction point, the town gas flow branches off to the twenty-firstflow path (75) and to the twenty-second flow path (77).

The town gas having flowed into the twenty-first flow path (75) flowstherein and arrives at the junction point of the twenty-first flow path(75) and the twenty-fourth flow path (81). And the town gas is mixedwith a fuel re-circulation gas at the junction point.

A source gas which is a mixture of the town gas and the fuelre-circulation gas flows in the twenty-first flow path (75) and arrivesat the junction point of the twenty-first flow path (75) and thetwenty-fifth flow path (83). And at the junction point, the source gasis mixed with the air flowed through the twenty-fifth flow path (83).

The source gas/air mixture enters the inside of the prereformer (5) viathe twenty-first flow path (75). And by the flowing of the sourcegas/air mixture through the catalytic part of the prereformer (5), theforegoing partial oxidation reaction is caused to take place.

A partial oxidation gas which contains CO and H₂ generated as a resultof the flowing of the source gas/air mixture through the prereformer (5)enters the inside of the fuel chamber (39) via the twenty-sixth flowpath (85). And the partial oxidation gas flows through the fuel chamber(39), thereby preheating not only the fuel electrode (35) but also theelectrolyte (33).

On the other hand, the air having flowed into the twenty-seventh flowpath (87) flows therein and enters the inside of the air chamber (37).And the air flows through the air chamber (37), thereby preheating notonly the air electrode (31) but also the electrolyte (33).

The fuel cell (7) is preheated until the time when the temperature ofthe fuel cell (7) rises to 500 degrees Centigrade.

Start of Electrical Power Generation

Next, the generation of electrical power is started while the fuel cell(7) is being preheated continuously.

Here, the third startup burner (12) is stopped when the temperature ofthe fuel cell (7) rises to 500 degrees Centigrade. At this time, theseventh and ninth electromagnetic valves (97,101) are placed in the openstate, while the eighth and tenth electromagnetic valves (99,103) areplaced in the closed state.

The source gas/air mixture enters the inside of the prereformer (5) viathe twenty-first flow path (75). And by the flowing of the sourcegas/air mixture through the catalytic part of the prereformer (5), theforegoing partial oxidation reaction is caused to take place.

A partial oxidation gas which contains CO and H₂ generated as a resultof the flowing of the source gas/air mixture through the prereformer (5)enters the inside of the fuel chamber (39) of the fuel cell (7) via thetwenty-sixth flow path (85).

On the other hand, the air having flowed into the twenty-seventh flowpath (87) flows therein and enters the inside of the air chamber (37).

Thereafter, in the fuel cell (7), the same electrode reaction asdescribed above takes place. Thereby, the generation of electrical poweris carried out.

In addition, the fuel cell (7) is preheated by the heat held in thepartial oxidation gas, the heat held in the air, the heat generated atthe time of the generation of electrical power. The fuel cell (7) ispreheated until the time when the temperature of the fuel cell (7) risesto 700-1000 degrees Centigrade.

Normal Operation of Fuel Cell Electrical Power Generation System

Next, the fuel cell electrical power generation system (1) performs itsnormal operation.

The third startup burner (12) remains still in the stopped state whenthe temperature of the fuel cell (7) rises to 700-1000 degreesCentigrade. In addition, at this time, the seventh electromagnetic valve(97) is placed in the open state, while the eighth, ninth and tenthelectromagnetic valves (99,101,103) are placed in the closed state.

A source gas which is a mixture of the town gas and the fuelre-circulation gas enters the inside of the prereformer (5) via thetwenty-first flow path (75). And in the prereformer (5), the samemethanation reaction as described above takes place.

A fuel gas which contains CH₄ and H₂O generated as a result of theflowing of the source gas through the prereformer (5) enters the insideof the fuel chamber (39) via the nineteenth flow path (62).

On the other hand, air enters the inside of the air chamber (37) via thetwenty-third and seventh flow paths (79, 87).

Thereafter, in the fuel cell (7), the same steam reforming and electrodereactions as described above take place. Thereby, the generation ofelectrical power is conducted.

Incidentally, when the source gas/air mixture is burned, water and sootmay be generated as a result of the burning of hydrocarbons contained inthe source gas. Accordingly, when the combustion gas is supplied to thefuel chamber (39) and to the air chamber (37), there is a possibilitythat the fuel and air electrodes (35) and (31) may deteriorate by waterand soot contained in the combustion gas.

In the present embodiment, the first heat exchanger (93) effects heatexchange between the combustion gas flowing through the twenty-eighthflow path (89) and the air flowing through the twenty-fifth flow path(83); and during the startup phase of the prereformer (5) and during thestartup phase of the fuel cell (7), the air heated by the first heatexchanger (93) is supplied to the prereformer (5) via the twenty-fifthand first flow paths (83, 75) while being supplied to the air chamber(37) via the twenty-fifth and seventh flow paths (83, 87). As a resultof such arrangement, water/soot contained in the combustion gas issupplied neither to the fuel electrode (35) nor to the air electrode(31). Therefore, both the fuel electrode (35) and the air electrode (31)are prevented from undergoing deterioration by water and soot.

In addition, during the startup phase of the prereformer (5) and duringthe startup phase of the fuel cell (7), the air heated by the first heatexchanger (93) is supplied to the prereformer (5) via the twenty-fifthand first flow paths (83, 75) while being supplied to the air chamber(37) via the twenty-fifth and seventh flow paths (83, 87). Sucharrangement makes it possible to raise the temperature of theelectrolyte (33) by making use of the heat held in the partial oxidationgas, the heat associated with the electrode reaction and the heat heldin the air heated by the first heat exchanger (93). Therefore, thelength of time until the temperature of the fuel cell (7) rises to itsoperating temperature is reduced further. Accordingly, the length oftime taken to activate the fuel cell (7) is reduced further.

In the present embodiment, it is arranged such that the air heated bythe first heat exchanger (93) is supplied to both the prereformer (5)and the air chamber (37); however, it suffices if the heated air issupplied to at least either one of the prereformer (5) and the airchamber (37).

Other Embodiments

In each of the aforesaid embodiments, precious metal catalysts, formedof Ru, Rh etcetera, are used to constitute the catalytic part of theprereformer (5). However, catalysts of the Ni family may be used.

In each of the aforesaid embodiments, the town gas is used as a sourcegas. However, the source gas may be natural gas, methanol, and coal gascontaining naphtha and carbon monoxide.

In each of the aforesaid embodiments, the fuel cell is constituted bythe solid electrolyte fuel cell (7) of the internal reforming type.However, the fuel cell may be any type of solid electrolyte fuel cell inwhich the above-mentioned steam reforming reaction does not take placewithin the cell.

INDUSTRIAL APPLICABILITY

As described above, the fuel cell electrical power generation systemformed in accordance with the present invention is useful when appliedto an electrical power generation system provided with a solidelectrolyte fuel cell. Particularly, the fuel cell electrical powergeneration systems of the present invention are suitable for reducingthe length of time taken to activate such a solid electrolyte fuel cell.

1. A fuel cell electrical power generation system comprising: a reformer(5) through which an oxygen-containing gas and a source gas are flowedand which has a catalytic part for causing the partial oxidation ofhydrocarbons contained in said source gas, and a solid electrolyte fuelcell (7) which is disposed downstream of said reformer (5) and which hasa cell main unit which includes: a fuel electrode (35) which is suppliedwith a partial oxidation gas which contains hydrogen generated as aresult of the flowing of said source gas and said oxygen-containing gasthrough said reformer (5); an oxygen electrode (31) which is suppliedwith an oxygen-containing gas; and an electrolyte (33) which liesbetween said fuel electrode (35) and said oxygen electrode (31), whereinan electrode reaction of said partial oxidation gas and saidoxygen-containing gas is caused to take place in said fuel electrode(35), said oxygen electrode (31) and said electrolyte (33).
 2. A fuelcell electrical power generation system comprising: a reformer (5)having a catalytic part which when a source gas is flowed therethroughconverts hydrocarbons, contained in said source gas and having a carbonnumber equal to or greater than 2, into methane under the presence ofhydrogen, and which when an oxygen-containing gas and said source gasare flowed therethrough causes the partial oxidation of hydrocarbonscontained in said source gas, and a solid electrolyte fuel cell (7)which is disposed downstream of said reformer (5) and which has a cellmain unit which includes: a fuel electrode (35) which is supplied with ahydrogen-containing gas; an oxygen electrode (31) which is supplied withan oxygen-containing gas; and an electrolyte (33) which lies betweensaid fuel electrode (35) and said oxygen electrode (31), wherein anelectrode reaction of said hydrogen-containing gas and saidoxygen-containing gas is caused to take place in said fuel electrode(35), said oxygen electrode (31) and said electrolyte (33), said fuelcell electrical power generation system performing: a startup operationin which said source gas and said oxygen-containing gas are flowedthrough said catalytic part of said reformer (5), and a partialoxidation gas which contains hydrogen generated as a result of theflowing of said source gas and said oxygen-containing gas through saidreformer (5) is supplied to said fuel electrode (35) as saidhydrogen-containing gas, and a normal operation in which said source gasis flowed through said catalytic part of said reformer (5) and a fuelgas which contains methane generated as a result of the flowing of saidsource gas through said reformer (5) is supplied to said fuel electrode(35).
 3. The fuel cell electrical power generation system of claim 1 orclaim 2 further comprising: first heat exchange means (6) for performingheat exchange between said source gas and said oxygen-containing gasprior to their entry into said reformer (5) and said partial oxidationgas discharged out of said reformer (5).
 4. The fuel cell electricalpower generation system of claim 1 or claim 2 further comprising: firstcombustion means (4) for burning said source gas and saidoxygen-containing gas during the startup phase of said reformer (5), andfirst combustion gas supply means (16) for supplying to said reformer(5) a combustion gas generated as a result of the burning of said sourcegas and said oxygen-containing gas in said first combustion means (4) sothat said reformer (5) is heated.
 5. The fuel cell electrical powergeneration system of claim 1 or claim 2 further comprising: secondcombustion means (8) for burning said source gas and saidoxygen-containing gas before said electrode reaction starts takingplace, and second combustion gas supply means (57, 59) for supplying tosaid oxygen electrode (31) a combustion gas generated as a result of theburning of said source gas and said oxygen-containing gas in said secondcombustion means (8) so that said oxygen electrode (31) is heated. 6.The fuel cell electrical power generation system of claim 1 or claim 2further comprising: third combustion means (12) for burning a source gasand a first oxygen-containing gas, second heat exchange means (93) forperforming heat exchange between a combustion gas generated as a resultof the burning of said source gas and said first oxygen-containing gasin said third combustion means (12) and a second oxygen-containing gasdifferent from said first oxygen-containing gas, and oxygen-containinggas supply means (75, 83, 87) for supplying to either or both saidreformer (5) and said oxygen electrode (31) said secondoxygen-containing gas heated by said second heat exchange means (93).